--- a/gcc/testsuite/gcc.dg/cpp/isysroot-1.c	Thu Oct 25 07:37:49 2018 +0900
+++ b/gcc/testsuite/gcc.dg/cpp/isysroot-1.c	Thu Feb 13 11:34:05 2020 +0900
@@ -1,10 +1,17 @@
 /* { dg-options "-isysroot ${srcdir}/gcc.dg/cpp" } */
 /* { dg-do compile  { target *-*-darwin* } } */
 
-#include <stdio.h>
+/* For the test to succeed there needs to be some header that is to be found
+   in the 'expected' place i.e. <sysroot>/usr/include/.  It's important that
+   it is not the name of a header for which fixincludes have been applied,
+   since such headers will be found in the gcc include-fixed dir and, in
+   general, reference additional headers.  The dummy sysroot will prevent the
+   additional headers from being found, resulting in a failed test.  So use
+   a header name we don't expect to see. */
+#include <example.h>
 int main()
 {
-  /* Special stdio.h supplies function foo.  */
+  /* Special example.h supplies function foo.  */
   void (*x)(void) = foo;
   return 0;
 }